docs: def hourly_relative_humidity(self):
          """A data collection containing hourly relative humidity over they day."""
          dpt_data = self._humidity_condition.hourly_dew_point_values(
              self._dry_bulb_condition)
          rh_data = [rel_humid_from_db_dpt(x, y) for x, y in zip(
              self._dry_bulb_condition.hourly_values, dpt_data)]
          return self._get_daily_data_collections(
              fraction.RelativeHumidity(), '%', rh_data)